I would highly suggest to subscribe to this Amortization Calculator. This is CFPB Regulation Z compliant loan amortization calculator with actuarial-grade APR calculations. Features Newton-Raphson method, multiple calculation standards (Actual/Actual, 30/360), and all payment frequencies (weekly, bi-weekly, semi-monthly and monthly). Built for financial institutions requiring Truth in Lending Act compliance and regulatory examination readiness. Enterprise-grade JSON responses with comprehensive error handling for fintech applications.

https://rapidapi.com/boltstrike1-boltstrike-default/api/boltstrike-loan-amortization-calculator1

You can enter actual dates and have variable first payment dates also - alongside different payment frequencies.

Very simple to use through RapidAPI